Pittsburgh's predominantly left-handed rotation picked up another right-handed candidate Thursday when the Pirates signed free agent Tony Armas to a one-year deal with a club option for 2008.

Terms of the contract were not revealed by Dave Littlefield, the Pirates' senior vice president and general manager. Armas made $2.26 million last season for the Washington Nationals.

"We had a situation last year where [former Pirates right-hander] Kip Wells got hurt in Spring Training and [Oliver] Perez struggled, so we wound up having to lean on the young guys, who although talented, it was very difficult to put all of that weight on their shoulders," Littlefield said. "We felt like we needed some experience as well as depth.

"Armas, while still young, he's experienced and maybe he has a chance to get back to where he was talent-wise as he gets farther away from the surgery."

Armas, 28, went 9-12 with a 5.03 ERA in 30 starts for the Nationals last season, his third season since undergoing rotator cuff surgery on May 23, 2003. He has increased his innings each of the last three seasons and his 30 starts in 2006 were four shy of the career high Armas set in 2001.

"He's increased his workload each year since his surgery," Littlefield said. "Like a lot of guys who have surgery, he's shown improvement the farther he gets away from the surgery. We felt like the one-year commitment plus the option was something that made sense for us."

The rotation is expected to be led off by left-hander Zach Duke and right-hander Ian Snell, but beyond those two the other leading candidates are three lefties -- Tom Gorzelanny, Paul Maholm and Sean Burnett -- and right-handers Shawn Chacon and Armas.

Marty McLeary, Yoslon Herrera and two other right-handed prospects, Bryan Bullington and John Van Benschoten, are also expected to be competing for spots when Spring Training begins.

Armas, who throws a sinking fastball that tops out in the low 90s in addition to a slider, changeup and curveball, is expected to compete with Chacon for the fifth spot in the rotation.

Armas enjoyed some success against Pittsburgh's competition in the National League Central last year. He was 1-1 with a 5.88 ERA against Houston, but fared much better against the other NL Central teams, going 4-0 with a 1.44 mark in five starts against the Cubs, Cardinals, Brewers and Reds. He was 2-0 with a 1.50 ERA in a pair of starts at Milwaukee's Miller Park and Busch Stadium in St. Louis. Armas did not pitch against the Pirates last year.

"I did notice [Armas' success against NL Central foes]," Littlefield said. "It's good obviously, but I'm leaning more on the fact that he's continued to make strides each year."

Armas' experience and penchant for being difficult to steal against will also help his chances to crack the rotation. He has a quick move to the plate and opposing players stole only 11 bases in 154 innings against him last season.

The native of Venezuela made his Major League debut with Montreal in 1999 and is 48-60 with a 4.45 ERA in 151 starts in his eight-year career.

To make room on the 40-man roster for Armas Jr., the Pirates designated right-handed pitcher Franquelis Osoria for assignment.

Armas might not be the last arm Littlefield adds before the club reports to Bradenton, Fla., for Spring Training. The GM has been talking trade possibilities with other teams and is also considering some of the free agents still on the market.

"I've been in discussions with several free-agent pitchers," Littlefield said.